The long term objective of this research is to understand the mechanism of ciliary and eukaryotic flagellar motility. Progress toward this goal requires more detailed new knowledge of the molecular organization and function of dynein ATPases which compose the arms of the peripheral microtubules of the 119+211 axoneme, and provide for directed cytoplasmic transport along microtubules. (Gibbons, 1987. Nature. 330:600). The significance of the work derives from the ubiquity of cilia and flagella and from related dynein-microtubule dependent cytoplasmic transport systems. Furthermore, these data are fundamental to precise description of the molecular basis of human ailments involving dynein (e.g. immotile cilia syndrome, fertility problems, and secretory, endocytic, and axonal transport defects). The approach is physiological and structural. New questions about the molecular organization, mechanism and regulation of dynein will require continued use of high resolution electron microscopy in combination with continued development of the new in vitro motility assay in which purified microtubules glide upon dynein surfaces, and by which the function and regulation of dynein can be reconstructed from purified components. The goals are to: (1) further characterize the in vitro motility assay with which we are able to directly study motile properties of purified dynein components, (2) characterize the regulation of outer arm dynein using the in vitro microtubule gliding assay, (3) determine the structural and functional proper-ties of isolated subunits of the outer dynein arms by microtubule binding and motility assays, (4) determine the molecular organization and functions of the inner dynein arms using cloned mutant Chlamydomonas cells defective in inner dynein arm subsets. The experimental approaches described are very productive and among the most promising by which to answer the questions posed. The data will complement that from other labs using genetic, kinetic, and molecular approaches in our common effort to understand dynein and its role in the axoneme.